1. Field of the Invention
The present invention relates to an X-ray tube, and more specifically to a fixed-anode-type X-ray tube whose anode is fixed.
2. Description of the Related Art
In conventional technologies, typical X-ray tubes include a fixed-anode-type X-ray tube. In the fixed-anode-type X-ray tube, electrons are generated by a filament of its cathode. These electrons are accelerated toward the anode target by a high-voltage electric field, and the high-energy electrons collide with the anode target to produce X-rays.
Heat is generated when the high-energy electrons collide with the anode target. The fixed-anode-type X-ray tube is provided with a cooling system of an insulating oil immersion type, a liquid forced cooling type, an air forced cooling type or the like in order to dissipate the generated heat into the outside.
In an X-ray tube of the insulating oil immersion type, a cathode assembly and an anode assembly are vacuum-sealed in an outer glass casing. The vacuum envelope is arranged inside a housing that is filled with insulating oil. The insulating oil serves as an electrical isolator and also as an absorber of heat generated in the anode assembly. The heat absorbed by the insulating oil is dissipated through the outer wall of the housing into the air.
In addition, as disclosed in Jpn. UM Appln. KOKOKU Publication No. H1-32720, for example, an anode target in an X-ray tube of a liquid forced cooling type is supported by a cylindrical anode supporting member. A cooling path is constituted by the inner space of the anode supporting member, through which a cooling liquid can flow to cool the anode portion.
Furthermore, as disclosed in Jpn. PCT National Publication No. 2001-504988, in an X-ray tube of an air forced cooling type, a vacuum envelope is constituted by an outer vacuum casing provided at one end thereof and an outer insulating casing provided at the other end. The anode supporting member has one end supporting the anode target and the other end extending from the other end of the outer insulating casing to the outside. A lead for supplying a high voltage to the anode target is connected to the other end of this anode supporting member. The outer surface of the outer insulating casing and the other end of the anode supporting member are wrapped with a potting material, namely molded material. For the purpose of cooling the anode portion, air is forced to travel outside the potting material.